Recently cameras using solid-state image sensors, such as video cameras, digital still cameras and cameras for broadcasting, and image pickup devices, such as cameras using silver halide film, are improving in terms of functions and downsizing. As an imaging optical system used for these image pickup devices, a zoom lens of which total lens length is short and resolution is high is demanded. As a zoom lens to satisfy these demands, a zoom lens comprising, in order from an object, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, which performs zooming by moving each lens group, has been proposed (e.g. see Japanese Laid-Open Patent Publication No. 2009-210691).
However these conventional zoom lenses have a problem, that is the zoom ratio cannot be increased while maintaining excellent optical performance.